For me, there are two companies I'd like to work for or build in my life time: Personalized Health Care and "moonshot" infrastructure projects (for lack of better wording).
Personalized Health Care - I'd love to work at a company that helps people be rid of diseases for an affordable cost. Ideally, we'd make big bets on understanding the genetic makeup of individuals and create drugs/therapies based on that make up. This would probably combine some interests of mine such as supercomputing, machine/deep learning, biotechnology, and a modern healthcare system to achieve this.
"Moonshot" Infrastructure - This is sort of similar to the Hyperloop stuff in a way. I think I'd really like to be part of a company that helps build the vision of what we thought it would be like when we grew up. Not necessarily flying cars but modernized & rapid transportation systems, incredible carbon-neutral buildings, robotics, etc.
Seems like my theme would be build the future I thought we'd have. Any company that contributes in a substantial way to progressing us towards something better than we had today, something meaningful, something memorable.